Observation and prediction of bottom collapse and middle break phenomena in the blasting demolition of high chimneys.

In order to solve the key problems affecting the safety of the project, such as the collapse of the support part and break in the air of the reinforced concrete chimney during the blasting demolition, this paper carried out systematic monitoring and theoretical analysis based on the 180 m chimney demolition project. Based on the characteristics of the stress-strain carve of concrete, the progressive failure mechanism of the supporting part under blasting load is revealed, the static equilibrium equation considering the stress-strain distribution of the section is established, and the chimney instability discriminant model with the ratio of gravity moment to resistance moment as the core is proposed. The fracture dynamic model of the chimney above the blasting notch is further constructed, and the propagation characteristics of stress wave and the amplification law of dynamic strain along the elevation under impact load are clarified. The research shows that the support part is prone to compression failure under large eccentric compression, and the minimum residual bearing capacity must not be lower than the weight of the chimney, which is the key to prevent collapse. The dynamic strain in the middle of the chimney caused by the touchdown impact is higher than that at the bottom, and the elevation amplification effect increases with the increase of the chimney height, resulting in the most dangerous section position migrating from the middle and lower part to the middle and upper part. The instability criterion and fracture mechanism proposed in this study have important theoretical support and engineering guidance value for the safety control of blasting demolition of high-rise structures.